1. Field of the Invention
The invention relates to a gas-cooled electrical machine.
The invention is based on a prior art as is disclosed, for example, in EP-0 519 091 B1.
2. Discussion of Background
In electrical machines with an indirectly cooled stator winding, the end links and the so-called round connections or phase connections connected to them in the winding overhang are cooled by a flow element of the cooling gas flow produced by the fan. In limit-rating machines, the end links and the phase connections are at risk of excessive heating. While the part of the winding embedded in the winding slots is cooled specifically, these exposed winding parts are heated not only by the current flow but also by the magnetic fields in the winding overhang area.
In rotating electrical machines with a directly cooled stator winding, the winding is composed of solid and hollow conductor elements, and in some machine types even just of hollow conductors. The coolant, which flows through the hollow conductors throughout the entire length of the stator bars, also results in the bars in the winding overhang being sufficiently cooled in this case. The round connections or phase connections are likewise designed as hollow conductors and are force-cooled by means of coolant.
In air-cooled machines and machines fed at one end, the cooling effect is no longer sufficient, particularly if the machine lengths are large. Thus, in order to improve the cooling effect, EP-0 392 243 B1 proposes that the winding bars, which are constructed from massive conductor elements, be provided with metallic cooling tubes/cooling channels located at the sides or between the two stacks of conductor elements. These are insulated from one another and from the conductor elements, and are located within the main insulation. They are supplied from both machine ends and from the machine center. The supply in the machine center is in this case provided by radial channels in the laminated stator core and openings in the main insulation. The heated cooling gas leaves the cooling channels through openings in the main insulation in the region of the end zones of the laminated stator core, and through radial channels in the laminated stator core.
Equipping stator winding bars with additional channels, and introducing such channels in the bar, reduces the slot filling factor. The moldings used for the input and output of the cooling gas, the majority of which are embedded in the main insulation, increase the manufacturing cost of the rods. In addition, no consideration is given to cooling of the round connections arranged in the winding overhang.
EP-0 519 091 B1 discloses a gas-cooled electrical machine in which only the metallic eyes used for the electrical and mechanical connection are specifically cooled. There, the eyes are provided with caps which virtually completely surround the eyes, leaving free one or more channels which run approximately axially. These channels are open toward the laminated stator core. A radially running bulkhead wall separates the winding overhang area from the induction area of the machine fan. At their ends on the bulkhead wall side, the caps have an opening, which is freely connected to the channels. A flexible pipe leads directly from this opening into the induction area of the fan. Because of the pressure difference between the induction area and the winding overhang area, part of the flow of the coolant produced by the fan flows through the channels and cools the eyes and, to a minor extent, the outermost bar ends as well. It could be regarded as being disadvantageous that the eyes are cooled by cooling gas which has already been heated as it flows through the end links in the winding overhang, that is to say a limited cooling effect is obtained.